Coupled circuit system



ixg.- 22, 1939. o. M. DUNNING E-r AL COUPLED CIRCUIT SYSTEM Filed March 20, 1935 2 Sheets-Sheet l NVENTOR M DUNN/NG CHA Es T. JACOBS E A TTORNE Y Aug. 2v2, 1939. o. M. DUNNING ET AL 2,170,048

COUPLED CIRCUIT SYSTEM Filed March 20, 1935 2 Sheets-Sheet 2 /Nl/ENTo/e ORL/ILLE M DUNN/NG CHARLES 7T c/Tqcoes LLM..

C .4 TTU/ENE y Patented Aug. 22, 1939 UNITED STATES PATENT OFFICE Jacobs, New Providence Township,

Union County, N. J., assignors to Thomas A. Edison, Incorporated, West Orange, N. J., a corporation of New Jersey Application March 20, 1935, Serial No. 11,956

3 Claims.

This invention relates to systems of coupled circuits, and more particularly to the suppression or elimination of undesired effects on the circuits from various potentials impinging or tending to impinge thereon from outside sources. The invention is particularly concerned with dynamic potentials the dynamic potential of an object comprising the fiuctuations (for example, periodic) in its .absolute potential. It

will be appreciated that two objects between which exists only a steady direct voltage, whether of Zero or finite value, and no matter how the absolute potentials of the objects may jointly vary, will have the same dynamic potential;

l5 While different dynamic potentials are necessarily possessed by any two objects between which a fluctuating or alternating voltage could be measured.

It is a broad object of our invention to suppress or eliminate the effect, on the circuits and each circuit of a system of the class described, of a plurality of different dynamic potentials impinging or tending to impinge thereon.

It is an allied object of our invention to suppress or eliminate the effect on the circuits of a plurality of different dynamic potentials respectively impinging or tending to impinge thereon.

It is another object of our invention to provide a system free or substantially free of undesired effects from a plurality of different dynamic potentials impinging or tending to impinge thereon.

It is still another object to provide .an im.- p-roved transformer for coupling together circuits having diiferent extrinsic dynamic poten- Another object is the provision of improved shielding means in such a transformer.

Still another object is the prevention of iiux generation in the core of the transformer by cur- .m rents produced in the shielding means as a result of different dynamic potentials acquired by those means,

Yet another object is the provision of improved means for shielding the circuits and sys- .17, tem generally.

Other and allied objects will more fully appear from the following description and the appended claims.

In the description reference is had to the ac'- 50 companying drawings, of which:

Figure 1 is a view, cross-sectional as to the coupling medium and schematic as to the rest of the circuits, of a coupled circuit system to which our invention has been applied in simple form;

|55y Figure 2 is a cross-sectional View taken verti- (Cl. Z50-16) cally through the coupling medium of Figure l, along the line 2 2 of that figure;

Figure 3 is a plan view of a circuit coupling medium in the form of a closed core transformer;

Figure 4 is a cross-sectional View taken along the line '1 -Il of Figure 3, illustrating not only the transformer but also the balance (the latter schematically) of a system to which our invention has been applied in preferred form;

Figure 4a is a view generally similar to Figure l0 e, but for convenience showing the transformer of Figure 4 only diagrammatically, and illustrating a modification of Figure 4 in respect of the circuit shielding means;

Figure 5 is a cross-sectional View taken along l5 the lines 5--5 of Figures 3 and 4;

Figure 6 is an enlarged end view of one of the shielded windings of the transformer of Figures 3, 4 and 5; and l Figure 7 is an enlarged plan View of a winding 20 shielded in an alternative manner and appropriate for use in place of one or both of the shielded windings shown in the transformer of Figures 3,

4 and 5.

A circuit point (or plurality of electrically 25 identical circuit points) exposed either conductively (by an actually connected path) or electrostatically (by an inherent capacitative path) to an external object or device will tend to acquire the potential of that object; if the point 30 is exposed to a plurality of external objects of differing dynamic potentials, it will tend to acquire a super-position of their dynamic potentials. The dynamic potential acquired by the point as a result of either such exposure may be termed extrinsic-i. e., resulting from an external influence. A whole circuit (comprising a plurality of electrically non-identical points) will acquire a single extrinsic dynamic potential if the exposure of all its points to external objects is only to one object or to a plurality of objects wth mutually similar dynamic potentials. And while .a Whole circuit may acquire a plurality of different extrinsic dynamic potentials at several of its electrically non-identical points from respective external objects of differing dynamic potentials, such a condition is objectionablein that spurious potential differences are created Within the circuit to co-mingle their effect with those of the intended, or intrinsic, potential differences within the circuit.

When a circuit has .acquired an extrinsic dynamic potential at one point therein from an external object, and an electrically distinct point of the circuit is electrostatically exposed to a second external object of different dynamic potential, it is common to interpose a conductive shield in the exposing path; to render the shield effective, it is ordinarily connected by la. path of negligible impedance to the rst circuit point or the rst external object. Electrostatic exposures to external objects of still other points of the same circuit are of course coped with by further shields similarly connected and/or by an appropriate extension of the first shield.

While such electrostatic shielding of a single circuit is well understood, we have found that special problems arise in connection with coupled circuits when the conditions under which the circuits operate entail the acquisition thereby of respectively different extrinsic dynamic potentials. These problems are occasioned largely by the capacities, within the medium coupling the circuits, between the members of the medium which are respectively connected in and form portions of the circuits and henlce have different extrinsic potentials. Considering any one coupling medium member, it will be appreciated that it is electrostatically exposed through these oapacities to the other memberseach of which is as to it, and as to each and every one of its exposed points, an external object of dynamic potential differing from its own extrinsic dynamic potential. A shield interposed between any two such coupling medium members, no matter where that shield be connected, is still ineffective to eliminate the exposure of at least one of the members to an object of dynamic potential different from its own extrinsic dynamic potential. Thus, if the shielding be left floatingi. e., not conductively connected anywhere-it will take on a dynamic potential intermediate the extrinsic dynamic potentials of the two members, to each of which the shield will therefore be an external object lof the mentioned undesirable nature. On the other hand, if the shielding be established at the extrinsic dynamic potential of either of the members, it is still as to the other member an external source of the same undesirable nature.

According to our invention there are interposed between adjacent coupling medium members two conductive shields; these shields are successively arranged, so that each electrostatically isolates the adjacent member from the other shield and the other member. Each shield is established at the extrinsic dynamic potential of the adjacent member, or in other words of the circuit containing that member. 'I'hus the only dynamic potentials tending to impinge on either member within the coupling medium may be restricted to the extrinsic dynamicv potential of that member itself.

Without intending thereby any unnecessary limitation of our invention, we have illustrated the same in connection with transformer coupling media, whose members adapted for connection in the respective circuits are coils or windings. A very sim-pie form of open core transformer has been selected for use in Figure l as a vehicle for illustration of our invention in simple form. In this figure this transformer is shown in cross-section longitudinally through the core, while the balance of the system of circuits is shown in purely schematic manner.

The two circuits are shown as I and 2 respectively, mutually coupled by the transformer T. Circuit I comprises for example the source 3 of signal or other oscillations to be transmitted by the system, the primary winding I I of the trans- Vbeen shown as three in number, two of them joining the extremities of the winding lI with the extremities of the source 3 and the third, 5c, joining the center of winding EI with the center of the source; while the leads 6 have been shown as two in number, joining only the extremities of the load l with the extremities of the winding I2.

The circuits I and 2 have different extrinsic dynamic potentials. Purely by way of non-limitative illustration of manners in which such potentials may be acquired by the respective circuits, we have shown in Figure l two extern-al objects 'i and 8 of diiferent jdynamic potentials (a potential relationship schematically indicated by the generator 9 of alternating voltage between these two objects); the object i being connected through negligible impedance to primary lead 5c and the object 8 being connected through a condenser' 8 to one of the secondary leads 6, which lead we have designated as 5b. Thus the primary circuit I acquires `an extrinsic dynamic potential at its lead 5c from the object '3, and the secondary circuit 2 acquires an extrinsic dynamic potential at its lead b from the object 8.

The transformer T comprises the central core I6; thereabout the primary winding II, surrounded lor encased by conventional insulation I3; thereabout the conductive shield 2|, preferably somewh-at overhanging the primary II on each end longitudinally of the core IB; about the shield 2| the layer of insulation I9; thereabout the conductive shield 22, for example of similar or a trifle greater longitudinal dimension to or than the shield 2l; and about the shield 22 the secondary winding I2, surrounded or encased by conventional insulation I 4 and preferably overhung on each end by the shield 22. The shield ZI, which may be termed the primary shield because of its adjacency to the primary winding I I, is established at the extrinsic dynamic potential ofthe primary circuit, as by connection thereof to the center-tap primary lead 5c, already mentionedras a point of acquisition of extrinsic dynamic potential by the primary circuit. Correspondingly the shield 22, which may be termed the secondary shield because of its adjacency to the secondary winding I2, is established at 'the extrinsic dynamic potential of the secondary circuit, as by connection thereof to the secondary lead Eb, already mentioned as a point of acquisition of extrinsic dynamic potential by the secondary circuit.

It will be noted that a capacity exists between the primary winding II and the core IB, so that the primary winding is exposed electrostatically not only to the shield 2l but also to the core. In order to insure that the core will not upset the condition of circuit I acquiring only a single extrinsic potential, the core may be connected as by lead Illa; to the primary lead 5c-i. e.,-posi tively established at the extrinsic dynamic potential of circuit I. This is not necessary, however, if the core has no electrostatic exposure to objects other than the primary winding I I.

A cross-sectional view of the transformer T,

taken transversely of the core I0, appears as 75 Figure 2. This illustrates the elements H, 2l, I9, 22 `and I2 each as of generally cylindrical formation. An important qualification, however, is to be noted as to the shields 2| and 22. While each of these is preferably of the full 360 degrees circumferential extension about the core, each must be provided in this extension with a discontinuity, so that it does not form a closed electrical turn about the core. Accordingly each shield may be formed of an originally flat, thin, conductive sheet, curved about the next inner element of the transformer and provided with a discontinuity in the form of a lap 2|' or 22' (corresponding to the designating numeral of the shield); the lap is formed by insulatedly overlapping the outer circumferential extremity 2l or 22 for a short distance over the inner circumferential extremity 2l" or 22"'. The insulation for each lap may be provided in any convenient manner, having been illustrated in each case as a narrow, thin strip l5 of insulation interposed between the shield extremities. In connection with the shields and with all of the insulation in Figures l and 2, it may be noted that their thicknesses have been materially exaggerated over those normally necessary, in the interest of illustration.

The structure of Figures 1 and 2 has been sufficiently described to set forth the feature of the two successive shields, each established at the extrinsic dynamic potential of the respectively adjacent winding or circuit. While this feature without further limitations may be suiciently efficacious satisfactorily to meet the conditions under which the circuits may be required to operate, we have found that under some conditions-particularly with larger amplitudes of effective generator 9 voltage-further structural limitations must be adhered to. These are described following a consideration of the manner in which the requirement therefor arises.

It is obvious that a substantial capacity exists between the two shields 2l and 22. Because of the different dynamic potentials of these shields, or alternating voltage therebetween, an alternating current will ow through this capacity. (Specifically as to Figure 1, this current may be alternatively identified as. that produced serially through the inter-shield capacity and the condenser 8 by the generator 9.) The capacity between the shields is distributed not merely longitudinally of the core, but also and more signicantly circumferentially thereof; therefore various portions of the current entering or leaving either shield through the respective lead 2la or 22a flow in the shield circumferentially to various extents-i. e., to extents of various fractional parts of a turn about the core (up to a possible maximum of substantially a full turn in the case of lead connection at either extremity circumferential of the shield). Such current iiow in each of the two shields will divide in opposite directions about the core (excepting of course in the extreme case of lead connection at a circumferential shield extremity) but we have found that with random relative arrangement of the laps 2| and 22 and/or of the points of connection to the shields of the leads 2|a and 22a and/or of the lap-to-lead relationships, the current flow in the pair of shields at one peak instant will almost invariably considerably preponderate in a first direction about the core, in the opposite direction at the next peak instant, and so on-in other Words, the pair of shields will constitute effectively some fractional part of a turn about the core for the alternating currents flowing from the generator 9. The traversal of this effective fractional part of a turn by these currents sets up a corresponding ux in the core i0 of the transformer, and thus induces a corresponding disturbing voltage in each of the windings of the transformer.

According to our invention we so mutually arrange the discontinuities or laps in, and points of connection to, the two shields as to balance out these shield currents in their flow about the core--in other words, as to render the pair of shields effectively an altogether negligible fraction of a turn about the core for currents from the generator 9. While it is possible to effect this net balancing wholly by balancing the current in one direction in one portion of each shield against the current in the opposite direction in another portion of the same shield, we have found the net balancing far more dependable if we alternatively or additionally balance the current now in each portion of one shield against the current flow in a respectively corresponding portion of the other shield. For illustration of an appropriate arrangement, reference is again invited to Figure 2.

Herein it will be seen that the points of connection of the leads 2id and 22a to the respective shields are in substantial radial alignment with each other. Further the outer circumferential extremity 2l of the primary shield-the extremity of that shield electrostatically exposed to the secondary shield-is in radial alignment with the inner circumferential extremity 22 of the secondary shieldthe extremity of that shield electrostatically exposed to the primary shield. Accordingly the shield currents enter and leave the transformer along the same radial line; and the innitesimal current portion which respectively ows through each' infinitesimal portion of the inter-shield capacity must traverse equal fractional turns in opposite directions in the respective shields. This effects balancing of the current in each portion of one shield against the current in a respectively corresponding portion of the other shield, and of course results in a thorough net balancing of the shield currents. This operational description must be mildly qualified by pointing out that it assumes the absence of any significant cross capacities in the neighborhood of the laps-i. e., capacity between shield portions respectively adjacent 2|" and 22, or respectively adjacent 2l" and 22"- or at least the substantial equality between these two cross capacities. Such assumptions are suite permissible in all normal cases, becoming almost rigorous when the mutually exposed extremities 2| and 22" are accurately aligned and when the thickness of the insulation I9 in the neighborhood of the laps is small and when, as illustrated and preferred but not indispensable, the extremities 2i" and 22 are pointed in the same circumferential direction. i

Additionally it may be noted that in Figure 2 the points of connection of leads 2id and 22a to the respective shields are each diametrically opposite the respective discontinuity or, in more precise terms, opposite that extremity of the respective shield which is exposed to the other shield (extremities 2l and 22")-an optional limitation which, when carried out either additionally to or in place of the balancing arrangement described in the preceding paragraph, re'- sults in a balancing of the current in that half of each shield which extends in one direction from the lead connection against the current in the other half of the same shield, these currents obviously flowing in opposite directions. rlhe reason why we prefer not to place entire or principal reliance on this second balancing arrangement is that its effectiveness is a function of the uniformity of the inter-shield capacity per small unit shield areaa characteristic which is not of innuence on the first described balancing arrangeg ment.

While the open core transformer represents a usable type for many purposes, and while because of itssirnplicity it forms an especially convenient vehicle for initial description of some of the funlgdainental features of our invention, the closed Till f -unusually severe.

core transformer remains a far more widely employed type. While our invention might to material advantage be incorporated in and with a closed core transformer in precisely the form illustrated for the open core transformer, there are certain refinements and other features which are desirably included when the closed core transformer is employed, as well as in any case wherein the operational requirements for the circuits. are Accordingly we proceed to a description of our invention in a refined form, ap plied to and with a transformer having a. closed core, for example of the shell type. This has been illustrated in Figures 3, e and 5, Figure 3 being :iosa plan View of a transformer U, the details of which appear in the cross-sectional Figures 4 and 5.

The primary and secondary circuits are again designated as l and 2, circuit i comprising the 35::source (for example a microphone), primary winding il, and leads 5 between the output tere minals 3 of source 3 and the electrical extremities of winding il; and circuit 2 comprising secondary winding iii, load 4 (for example the first tyg-stage of an audio frequency amplifier) and leads between the electrical secondary winding extremities and the load input terminals ii. The core of the transformer U is designated as iii?, having the central leg ll about which the priiaymary and secondary windings are concentrically disposed.

In these figures we have shown the primary and secondary winding shields not merely in successive interposition between the windings (as in Figures l and 2), but each completely encasing its respective winding (together of course with the insulation i3 or ill provided thereabout). One reason for this is that although the simple shield interposition eliminates the electrostatic exposure roi either winding to the opposite winding and the shield therefor so far as this exposure occurs (as it does principally) along straight lines, this exposure can also to a very restricted degree occur along curved lines, and to that degree is obviously :poorly guarded against by the structure of the first figures; under sufficiently severe operational conditions this becomes important. Another reason, peculiar to the closed core transformer and important as to at least all but one of the windings, is that the core, which of course must be ythe insulation i3 or lli for the respective winding,

and having its ends portions (considered in a di' rection axial of the winding) folded outwardly or away from the winding axis to lie against the ends of the winding insulation i3 -or i4; and an outer shield element (2in for the primary and 'imv for the secondary) extending circumferentially immediately outside of the respective insulation I3 or lli, and having its end portions folded inwardly or toward the winding axis to lie against and make electrical contact with the folded-over end portions of the respective inner shield element. Both inner and outer members. of each shield are provided with a discontinuity in the form of a lap (Zim, 2in', 22m and 22p for shield elements Zim, 2in, 22m and Z211, respectively), the laps in the inner and outer elements of each one shield being in radial alignment with each other and forming a continuous lap insulated by insulation which may be in the form of a strip or overlapping series of strips encircling the winding parallel to its axis; these strips are designated as l5 for the primary winding shield and 255 for the secondary winding shield.

The illustration of Figures 3, 4 and 5 as to this shieid structure encasing each winding is supplemented by Figure S--and enlarged end view oi one of the windings (arbitrarily the primary) and its inner and outer shield elements. The shield elements are conveniently of thin, soft copper foil or other like conductive material. In order to facilitate the outward folding of theend portions of the inner shield element Zim, longitudinal cuts di may be made in each end portion, dividing the same into a succession of tabs 43 which may be folded outwardly without difliculty and cemented against the ends. of the insulation i3. While the inward folding of the end portions of the outer shield element 2in may be similarly facilitated, the material of the shield element, if thin and soft, will readily fold inwardly without cuts and form within itself ridges or folds which wehavc illustrated as We have found that the oementing, by thin, sc-called household cement, of the folded-over portions of the outer shield element to those of the inner shield element does not, if well pressed out, interfere with the requisite electrical contact between the two shield elements. Figure d plainly illustrates the continuity of the laps Elm and 2in in the inner and outer shield elements respectively, achieved by cementing the insulating strip or series of strips H5 in place Vbefore the folding over of the end portions of the outer shield element is completed. It is. of course possible to form one of the shield elements (preferably the inner) without overhanging end portions, and simply to fold the end portions of the other shield element completely about the ends of the insulation i3 into overlapping contact with the rst shield element. It will be understood that the primary shielding structure so specicaily described with reference to Figure 5 may be identically followed in.` connection with the shielding of the secondary winding l2, the designating numerals being considered in each instance as greater by one than those appearing in Figure 6.

The transformer U, as illustrated in Figures 3 through 5, comprises the shell type core with its central leg element ll; thereabout a layer of insulation i6; thereover a generally cylindrical shield element 20m hereinafter referred to; thereover a layer of insulating Ilm; thereover the primary winding il, successively encased or surrounded by the insulation I3 and the shielding 2mn-2in as above described; thereover a 75 layer of insulation IIn; thereover a generally cylindrical Shield element 2011l hereinafter referred to thereover a layer of insulation I8; and thereover the secondary winding I2, successively encased or surrounded by the insulation I4 and the shielding 22m-2211, as above described. As will hereinafter appear, the employment of the shield elements 20m and 2071l is not indispensable, and the omission of both or either of these elements may be attended by the merging of the immediately adjacent insulating layer I'Im and/or I'In, as the case may be, into the respective insulating layer I6 and/ or I8.

In order that the primary and secondary leads (5 and 6 respectively) shall not, by inherent capacities to elements of the transformer, counteract or undo the effect of the complete shielding of each of the primary and secondary windings, at least their portions near the transformer should be shielded by shielding connected to the respective winding shielding. Accordingly we have shown about the respective leads conductive braid shielding 5s and 6s. This shielding may in each case enter the respective winding shielding, the inner and outer winding shield elements (Zlm and 2 In or 22m and 22m) being formed for a short distance along the braid shielding adjacent its point of entry and making electrical contact thereto. By this arrangement the lead shieldings may become the connecting leads (analogous to 2m; and 22a of Figure 1) for the primary and secondary winding shields. The application of fluctuating different potentials between the respective lead shieldings 5s and '6s is contemplated; but the typical means illustrated in Figure 4 by which this occurs is described at a later point in this specification.

Because of these fluctuating different potentials there will tend to occur, as in the case of transformer T of `earlier figures, a current flow between shielding elements of ythe transformer U. The latter transformer is conveniently considered at this point with the omission, which is permissible, of both the shield elements 20m and 201i. It will be seen that the exposed lap extremities. of the winding shield elements, and in particular those two (2In and 22m) which are mutually exposed, are in radial alignment with each other; that the points of connection to the two winding shields-i. e., of entry of the leads 5s and 6s thereinto-are in radial alignment with each other; and (as preferred but not essential) that the laps or discontinuities are arranged at least nearly diametrically opposite the respective points of lead connection. Thus those specifications which were shown desirable for the balancing of shield currents in connection with transformer T are observed in connection with transformer U. But in` transformer U there eX- ist additional opportunities for shield current flow. The outer portions of the core (i. e., other than the central leg element IID) form conductive elements which are respectively adjacent circumferentially different portions of the winding shields (e. g., portions at the ends of those shields and on the periphery of the secondary shield) and which have capacities to those portions; through any of these capacities across which a dynamic potential difference exists there may flow alternating currents which must pass through portions of the respective shields. We cope with the shield currents so arising by maintaining at least a moderate spacing of all winding shields from the outer core portions; by arranging the points of connection to the Winding shields ina 90 degree displacement from the plane f the core (i. e., midway circumferentially of the shields between corresponding shield-core capacities) and by maintaining as nearly similar as possible such respectively corresponding capacities (e. g., capacities symmetrically disposed about the line 4 4 in Figure 5). Thereby the shield currents through these capacities are maintained small and divide in opposite directions in each one shield member, and the mutually opposed flows are quite well equalized and satisfactorily balance each other. Of course the core may be established at the potential of the shield of one of the windings, as by connection thereof by lead I Ia to the secondary lead shielding 6s, rendering the shield current flow just discussed significant as to the other winding only.

The other described structure of a pair of shields interposed between two windings of the transformer, with particular arrangements of shield discontinuities and leads within the pair, is generically applicable for interposition between any two transformer elements having different dynamic potentials. Utility of this structure in other positions than simply between two windings may be found. For example, if the primary and secondary windings are separately formed and shielded, as hereinafter suggested as one method of construction, it may be difficult accurately to align the discontinuities of the two winding shields. In this case it is convenient to rely on only the rst of the winding shields as a member of the specially arranged pair; and to complete the pair by a further shield interposed between the winding shields, having its discontinuity and point of lead connection in proper relationship to those of the first winding shield, and established at the dynamic potential of the second winding shield. In this case the specially arranged pair becomes interposed between the f1rst winding and the second winding shield, and this shield may have its point of lead connection and its discontinuity randomly arranged with respect to those of the pair. We have illustrated such a further shield as the shield element 207i abovementioned; and while as illustrated it is appropriately arranged Within the transformer to form the specially arranged pair with either winding shield, it may be considered to have been accurately installed over the primary winding shield and to form the pair therewith.

While the discontinuity in the shield 20u, which we may term the intermediate shield, may of course be a lap as above described for other shields, we have found it permissible to employ for this shield a simplified gap discontinuity, wherein the circumferential extension of the shield is a trifle less than 360 degrees and the extremities of the shield are accordingly separated by a slight gap 201i. Proper alignment of this discontinuity with the adjacent lap discontinuity in the primary winding shield is provided by radially aligning the center line of the gap 201i' with the thereto exposed primary lap extremity 2m. The lead 20a for the intermediate shield, connected thereto in radial alignment with the point of connection of the primary shield lead 5s, is connected to the secondary lead shielding 6s. Because of the secondary winding shield potential thus acquired, and the interposition between the winding shields, the intermediate shield takes the place of the secondary winding shield as a conductor of inter-shield currents. In order to insure that the intermediate shield is quite effectively so interposed, we have made it materially to overhang the shielded primary winding on each end, so that curved as Well as straight lines wardly against this extended insulation.

The inner shield element (Zim) for the primary winding has a relatively large capacity to the core leg element iiD' which, while theoretically symmetrically distributed circumferentially, may not be so in practise-particularly if the core leg lits loosely or non-centrally within, the windings. When this primary shield is, as illustrated, at a different potential dynamically from the core, it is possible that the resulting shield currents therein to and from this capacity will, no matter where the point of lead connection to the primary winding shield be made, iiow unbalancedly through the shield element 2 im and set up an undesired flux in the core. As a pre- Ventive against this we may employ the shield 29m illustrated and abovementioned, interposed between the shield element Zim and the core leg element I iii', and forming with the shield element Zim a. specially arranged pair of shields such as abovementioned but interposed between the primary winding and the core leg' element. The shield 20m is generally similar to the shield Zim, having a corresponding gap or other dis.-

continuity Zilml in radial alignment with the thereto exposed lap .extremity Zim of the primary winding shield, having a lead 20h connected thereto at a point in radial alignment'with the point of lead connection to the primary winding shielding, and being thereby connected with the secondary lead shielding and hence with the core. 'Ihe shield 28m of course takes the place of the core leg element i i0' as: a conductor of' shield currents otherwise flowing to that element from the shield element 2 im, restricting these currents to the specially arranged shield pair Zim-23m wherein they will be properly balanced.

As illustrated, all of the elements of the transformer other than a first of the shielded windings (e. g., the primary winding iiA and itsl shielding Zim-2in) are established at the extrinsic dynamic potential of the other winding (e. g., the secondary winding i2); and shielding at that dynamic potential (e. g., shields Zilm inside and 291i outside the shielded primary winding) substantially isolates the first shielded winding electrostatically from all such other elements. It may be mentioned that under these circumstances, and depending on the stringency of the operational requirements for the circuits, it may be permissible to omit the shielding of the second winding (e. g., of secondary winding i 2) we have, however, generally preferred to retain the latter shielding in any event. Of course the electrostatic isolation of the shielded primary from all other elements of the transformer may be rendered not merely substantially but practically perfectly complete by folding over the end portions of the shields 20m and 207i into overlapping contact with each other against the ends of the shielded primary, the insulation i'im and/or i111, having first been folded over against the shielded primary ends andthe discontinuities in shields 20m and Zln being, as illustrated, in radial alignment with each other.

The transformer U being of novel nature, we

may supplement the detailed description of its,

entially thereabout flat insulating paper, such asf fish-paper, and securing at least the external extremity of the wind withv cement. The insulating layer iim has been formed by coiling similar paper into a4 small, loose tubular form and passing it axially within the shielded primary winding, thereupon expanding it into contact with the inside of the shielded winding and securing at least theinneror exposed extremity of the paper with cement. The proper circumferential length of the intermediate shield Zim to aord the slight gap 2 in' has been determined by test, and the soft, thin, conductive shield material cut to size and cemented over the insulating layer i 'inof course with its gap in proper alignment. The

proper circumferential length of the shield 261m.

has been similarly determined, and the shield material cut to size, coiled into small, loose tubular form, inserted inside the insulating layer iim, and expanded into contact therewith and cemented thereto. formed over the shield Zim similarly as was layer i'in over the shielded winding; and the insulating layer i5 has been formed within the shield 26m similarly as was layer i'im within the shielded winding. This has completed the pri-v mary assembly. The shielded secondary winding, formed with appropriate dimensions, has been slipped snugly over the primary assembly, and the transformer assembly completed by stacking of the core. this procedure, with the separate formation and shielding of the two windings as distinguished for example from a progressive outward winding and building up process from layer iii to outer secondary winding shield element 221i, is disclosed merely as one which we have actually employed and have thought to facilitate the proper formation of the primary and secondary winding shielding Zim-Zln and 22m-22m it is not disclosed with any limiting intention whatsoever.

While we have shown in Figures 3 through 6 and described above a construction of inner and outer shield elements (Zim and 2in or 22m and 2212) for fully encasing each of the two windings ii and i2, We do `not intend any limitation of the encasing shielding means for the windings to this particular construction. By way of illustration of an alternative means which we have employed, we have shown in Figure '7 a primary winding ii encased in shielding which is in the;

form of a strip Zip of thin, soft conductive material (for example copper)- toroidally wound about the winding i i (this of course being first insulated by its conventional insulation i3) after the fashion of the cloth tape frequently wound about a coil for mechanically binding it into a rigid unit. In the interest of illustration this strip 2 Ip is shown only fractionally-Wound about the primary winding ii. The initial extremity 2iq of the strip Zip may be cemented to the in--f The insulating layer i8 has been 1:,

It will be understood that* sulation I3 practically at one end of the winding II, and a first turn ZIT of the strip ZIp made about the winding Il so that inner and outer portions of the turn are quite parallel with the axis of winding Ii. Beginning with the second turn 25s, the turns are made slightly angularly with respect to the axis of winding II, so that the winding of the strip 2 Ip progresses toroidally about the primary winding II, but with each successive turn of the strip overlapping and contacting with the immediately preceding one. Before the winding of the strip ZIp is completed, the insulating strip or series of strips II5 (fractionally shown in Figure 7) is secured over the beginning circumferential extremity 2Ip" of the toroidal strip Zip winding, inside and outside of the primary winding li in quite similar fashion to the installation of the member IIS in earlier figures. The toroidal winding of the strip 2Ip is continued entirely about the winding I I, the final turn 2 it (fractionally shown) overlapping the strip I iii and therethrough the extremity 2Ip", and being arranged with inner and outer portions quite parallel with the winding II axis. This construction provides the insulated lap 2 Ip', having the exposed extremity Eip and it will be understood that in the assembly in the transformer of the winding shielded as just set forth, this lap and its exposed extremity will be arranged as set forth for the laps and their extremities hereinabove. in Figure 7 a small part of the forward portion of winding I i and insulation I3 has been broken away to show the rearward portion, with the shielding strip 2 ip thereabout and the entry of leads E- to the inding ii. These leads of course enter the winding shielding within the lead shielding 5S, the strip 2 lp in those of its turns appropriate thereto being formed around and making electrical contact with the lead shielding 5s.

It will be understood that while we have illustrated the windings herein as cylindrical, we intend thereby no unnecessary limitation whatsoever; the application of our invention to windings of such other or distorted cross-sections as squares or the like will be entirely obvious. It is also to be understood that by the term radial alignment herein we do not intend to imply any restriction of the aligned points or regions to a single line extending radially and normally away from the axis, but rather a restriction or Substantial restriction to a single plane containing and extending radially from the axis.

The description of Figures 3 et seq. may be completed by referring to the portions of the system other than the transformer U, which other portions in one arrangement have been shown in Figure 4, and in a modified arrangement in Figure 4a; the latter figure may first be referred to. A requirement for extrinsic dynamic potential difference between primary and Secondary circuits lias been assumed; and as a typical but non-limitative reason for this requirement, it may be considered thatJ the load 4 must be conductively connected to an external object 8 of dynamic potential differing widely from that of ground, While the primary shielding (and hence the primary circuit, whose extrinsic dynamic potential must follow that of its shielding) cannot be permitted to acquire a potential so dynamically different from ground potential (for example because of shock hazard). In accordance with these conditions the lower-shown input terminal 4 of the load i has been shown connected as by the connection 8o to object E. In order that the secondary circuit acquire but one extrinsic potential, its lead and winding shielding may also be connected to the object 8, as by lead 6a. Under severe operational conditions it is very probable that the outer portions of the leads 6 Will, if they remain unshielded, be sufliciently electrostatically exposed to some external source or sources of still other dynamic potentials to cause difficulty; accordingly We show a conductive shield 4s extending partially about the load 4, and the lead shielding 5s entering and electrically contacting with the shield 4s. The extent of the secondary circuit shielding means thus pro- Yided is intended to be suilicient to isolate the secondary circuit electrostatically from all objects of dynamic potential other than that of object 8 (this potential being the extrinsic dynamic potential of the secondary circuit, in view of the negligible impedance shield connection Ea and of the circuit connection Bo, whether of negligible or nite impedance) the secondary shielding is permitted, however, to expose electrostatically to the object 8 only, some point or points in the secondary circuit-such as the intermediate point 4" in the load li, through the inherent capacity 4.

To meet the outlined conditions the primary circuit extrinsic dynamic potential may be made the dynamic potential of ground, shown as Ig and from which the dynamic potential difference of the object 8 has been dottedly indicated by the generator 9. Thus one of the primary leads 5 (designated as 5b) may be connected as by lead iid with the lead shielding 5s, and the lead shielding as by lead 5e to ground. A shield 3s may be provided partially about the source 3, and entered and electrically contacted with by the primary lead shielding 5s, analogously to the arrangement described for the secondary circuit. Some unshielded point or points in the primary circuit may be assumed to be left electrostatically exposed by the composite primary shielding, but only to ground-such for example as the intermediate point 3 in the source 3, through the inherent capacity 3".

While the system as thus described will operate satisfactorily, it is frequently troublesome to connect the lead ec from the primary circuit and shielding to ground, particularly in the case of portable apparatus. If this connection be omitted, its place will be taken by the inherent capacity 'I' naturally existing between the primary shielding ground. Now the primary shielding will acquire a dynamic potential intermediate those of ground and of the object 8, to which two dynamic potential sources the primary shielding is exposed through the respective nte impedance paths of capacity I and the intershield capacity within the transformer U. The primary circuit is of course conductively exposed to the primary shielding through the lead 5d if this be retained, or electrostatically exposed through the large capacity between shielding and primary circuit if this connection 5d be omitted. But at the point 3" the primary circuit is electrostatically exposed to ground through the capacity 3. Accordingly, excepting in a purely fortuitous case, the primary circuit will acquire different extrinsic dynamic potentials at respectively different points, which cannot be permitted for reasons early above discussed.

It is to be understood that the exposed point 3 in the primary circuit is intended to be typical of any point or points so exposed in that circuit, and that its illustration as a point in the source 3 is by way of example only.

According to our invention in its preferred embodiment, as illustrated in Figure 4, we extend the shielding of the primary 'circuit so that it includes complete winding shielding as above described, complete lead shielding and complete source shielding such as conductive enclosure St encasing the source 3-in other words, so as` to provide complete encasement of the entire circuit in commonly conductive shielding means. This of course eliminates all electrostatic exposures of circuit points such as that of point 3" through the capacity 3". It will be understood that we use the term complete encasement in the sense of essentially complete electrostatic isolation; and that any encasement which provides such isolation, though penetrable by other forces than electrostatic, will be a satisfactory one. (Indeed, it is necessary if source 3'be a microphone that the enclosure St thereabout be acoustically penetrable, while remaining electrostatically essentially impenetrable; it may accordingly be of single or laminated relatively ne wire cloth.) By this complete circuit encasement we are enabled to leave the entire primary shielding oating-i. e., conductively unconnected to any external object-or to connect it to any external object which temporary convenience or apparatus requirements external to the circuits may dictate; conductive connection of the primary circuit to the primary shielding, as by lead 5d, being rei. tained or omitted at will. We may of course so completely encase the secondary circuit, as we have illustrated in Figure l by the substitution of the 'complete enclosure dt for the partial shields 4s of Figure 4a; but so long as the operating re- E quirements necessitate some conductive connection such as 8a from the. secondary circuit to the external object 8, the secondary shielding must be conduotively connected with the secondary circuit and that object, to one or the other by a connection of negligible impedance such as the lead .6a.

In the claims hereto appended we intend to claim the various novel combinations, sub-combinations and features which we have disclosed 45- as broadly as the state of the art will permit.

We claim: Y i 1. In combination, a plurality of closed circuits; a coupling medium having a plurality of members respectively included in said circuits; a plurality of conductive shields for isolating said members respectively within said coupling medium; and a plurality of shielding means at mutually diierent dynamic potentials Vand respectively associated with said circuits external to said coupling means, each of said conductive shields having the dynamic potential of the respective said shielding means, and each of said shielding means extending about its associated circuit suliiciently to limit the acquisition of extrinsic dynamic potentials by that circuit to the dynamic potential of that shielding means.

2. In combination, a closed circuit and a second circuit; a coupling medium having rst and second members respectively included in said circuits; first and second conductive shields for isolating said members respectively within said coupling medium; and lrst and second shielding means respectively at mutually different first and second dynamic potentials and respectively associated with said circuits external to said coupling means. said conductive shields respectively having said first and second dynamic potentials, and said iirst shielding means extending about said closed circuit suiiciently to limit acquisition of extrinsic dynamic potentials by that circuit to said iirst dynamic potential.

3. In a transformer system including a core element and two windings circumferential thereto, two conductive shields for said windings respectively, each. said shield extending between its respective winding and the other shield, and a third conduct-ive shield interposed between said two shields, each of the three shields being provided with a circumferential discontinuity and with connecting means, the discontinuities in and connecting means to said third shield and a rst of said two shie-lds being so arranged as to balance out uctuating circumierential shield cur.- rents produced by a difference of dynamic potential of those shields, and said third shield and the second of said two shields being at the same dynamic potential.

ORVILLE M. DUNNING. CHARLES T. JACOBS.

CERTIFICATE OF CORRECTION.

Patent No. 2,170,0MB. August 22, 1959.

ORVILIE M. DUNNING, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column,.1ine hh., for the word "source" read object; page 5, first column, line 5, strike out "the", line 18, for 22' read 22' and second 'co1- umn, line 56, for "suite" read quite; page )4, second column, line l, for ends read end; page 5, first column, lines 55 and 58 respectively, for "fluctuating" read fluctuatingly; page 6, first column, line 6, for faciltated" read facilitated; and second column, line 26, for "Zln'" read 20n'; and that the said Letters Patent should be readwith this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5rd day of October, A. D. 1959.

Henryl Van Arsdale, (Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2,170,0l4B. August 22, 1959.

ORVILIE M. DUNNING, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column,1ine 1411 for the word "source" read object; page 5, first column, line 5, strike out "the"; line 18, for 22' read 22' and second 'column, line 56, for "suite" read quite; page LL, second column, .line l, for "ends" read end; page 5 first column, lines 55 and 58 respectively, for "fluctuating" read fluctuatingly; page 6, first column, line 6, for "faciltated" read facilitated; and second column, line 26, for "Zln" read 20n'; and that the said Letters Patent should be readwith this correction therein that the same may conform to the record of the case inthe Patent Office.

Signed and sealed this 5rd day of October, A. Dv. 1959.

' HenryI Van Arsdale, (Seal) Acting Commissioner of Batents.' 

